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What PSI To Follow? #5259182 11/05/19 01:58 PM
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lancerplayer Offline OP
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I have an off road vehicle (Polaris Ranger) that specs the factory tires to be filled to 10 PSI for the front and 12 PSI for the rear. I got new tires put on that are 1" taller and the PSI rating on the tire says max PSI is 7. I had the intention of filling to the factory specs, but once I reached 7 PSI, the tire was firm enough that I didn't want to put more air in it.

What is the proper spec to follow in this situation?



Re: What PSI To Follow? [Re: lancerplayer] #5259196 11/05/19 02:20 PM
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Rmay635703 Offline
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Originally Posted by lancerplayer
I have an off road vehicle (Polaris Ranger) that specs the factory tires to be filled to 10 PSI for the front

I got new tires put on that are 1" taller and the PSI rating

What is the proper spec to follow in this situation?


There isn’t a spec when you use a different tire size.

In general if your vehicle needs XXXX LBS weight rating, your OEM tires are spec’d for a pressure to achieve that end.

Put on a different size and you need to inflate to the pressure needed to support the load, a larger tire generally should be able to support more weight at its sidewall rating.

So you should be covered.

It’s all about the weight rating and not the arbitrary pressure listed in the manual

Re: What PSI To Follow? [Re: lancerplayer] #5259208 11/05/19 02:44 PM
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JLTD Offline
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Tire max is tire max.


I use the overseas manual to choose my viscosity.

Using AMSOIL

Hers: 2008 Jeep Liberty 154k, SS 5w30/Amsoil

His: 2015 4Runner 60k, SS 5w20/Amsoil

Re: What PSI To Follow? [Re: lancerplayer] #5259257 11/05/19 04:25 PM
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krismoriah72 Online Content
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At Max PSI on those tires the ride is going to be more harsh than you are used to. Extra abuse will occur to suspension as well.


What tire? What Ply?

Re: What PSI To Follow? [Re: krismoriah72] #5259285 11/05/19 05:10 PM
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Rand Offline
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Originally Posted by krismoriah72
At Max PSI on those tires the ride is going to be more harsh than you are used to. Extra abuse will occur to suspension as well.

Did you read the post? OP went from 10/12 to 7 psi why would it be more harsh?

I would like to know what the load rating of the tire is.. seems like a 7psi 1" taller tire that isnt wider might not have enough load capacity.


2019 Jeep Cherokee Trailhawk 2.0T
2020 Hyundai Elantra "Value Edition"
Re: What PSI To Follow? [Re: Rand] #5259461 11/05/19 08:26 PM
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hallstevenson Online Content
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Originally Posted by Rand
Did you read the post? OP went from 10/12 to 7 psi why would it be more harsh?

I believe that in the OP's new tires, with a max PSI of 7, they will be "harsh" or hard or firm. It's relative to the max PSI of the tire. If you put 12 psi in your car tire, it wouldn't be "harsh", right ? No, because it's max will be 45-50 PSI or more.

Re: What PSI To Follow? [Re: hallstevenson] #5259487 11/05/19 09:01 PM
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Rand Offline
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Originally Posted by hallstevenson
Originally Posted by Rand
Did you read the post? OP went from 10/12 to 7 psi why would it be more harsh?

I believe that in the OP's new tires, with a max PSI of 7, they will be "harsh" or hard or firm. It's relative to the max PSI of the tire. If you put 12 psi in your car tire, it wouldn't be "harsh", right ? No, because it's max will be 45-50 PSI or more.


So with that said your theory would be a p-metric truck tire with 44psi(max 44 psi sidewall) would be more harsh than a load range e tire with 44psi(80psi on sidewall)

For simplification assume the tires are the same brand and model... cooper at3 etc.

I think your theory works on some tires but fails on others.

You have 2 relatively the same size tires in the OP's post one with 7psi is going to be a marshmallow compared a similar tire with 12psi regardless of the sidewall max pressure.. if anything the higher psi tire(higher psi on sidewall) will have more
extra ply sidewall and ride worse than the other tire at the same 7psi.


2019 Jeep Cherokee Trailhawk 2.0T
2020 Hyundai Elantra "Value Edition"
Re: What PSI To Follow? [Re: lancerplayer] #5259542 11/05/19 10:21 PM
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Sounds like you put the wrong load range of tires for it. Might be OK for an ATV, but not a heavy UTV. Find out the max load capacity of the old tires vs. the new ones.


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2000 Toyota Camry 2.2L 235k Mobil Super HM 10w40 & Fram Ultra
1996 Jeep Cherokee 4.0L 149k Mobil 1 HM 10w40 & Fram Ultra
Re: What PSI To Follow? [Re: lancerplayer] #5259704 11/06/19 07:03 AM
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The right way to do this is to match the load carrying capacity of the specified tires at the specified pressures - and if there is enough load carrying capacity, then match the inflation pressure to get the same spring rate (if possible!).

We only know half of the information - the inflation pressure.

I found the Polaris web site and looked up the tire sizes: 27X9-12 and 27X11-12. The Polaris web site indicates they specify Maxxis MU511 and MU52 tires - so I went to the Maxxis website and didn't find those designs.

So I looked at what they offered and while I found the sizes - and they listed the max load - they didn't list the corresponding pressure. But I did find out that the tires come in Ply Ratings

So I went to my Tire and Rim 2005 Yearbook to see if I could translate the max loads into Ply Rating - and my old book doesn't list those sizes. I guess I need to get a more current TRA Yearbook.

Lancerplayer: Please help me help you by telling me if I got the original tire size right, and what Ply Rating they were. Plus what the new size and ply rating is - AND where I can find the load tables for the tire sizes involved.

What disturbs me most is that there is a pressure split front to rear and unless we account for that, the vehicle could be a bit dodgy to drive - especially in emergency situations - and then it will be too late!!


CapriRacer

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Re: What PSI To Follow? [Re: lancerplayer] #5260422 11/07/19 04:52 AM
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Yes to the above, though much is less critical when dealing with an ATV/UTV.

If you have them & already on, I’d air them to the max of 7 psi(maybe 8) then try them out. I often like tires on my Honda ATV to be on the firm side. I just putz around, no need to emulate a NASCAR driver with what I do.

Re: What PSI To Follow? [Re: lancerplayer] #5266048 11/13/19 12:35 PM
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Re: What PSI To Follow? [Re: lancerplayer] #5266779 11/14/19 08:35 AM
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LancerPlayer,

Thanks for the additional info. Let's see if I have this right:

Old Front: 26X9-12 6 PR Specified inflation 10 psi
Old Rear: 26X11-12 6 PR Specified Inflation 12 psi

New Front: 25X8-12 4 PR Max Pressure 7 psi
New Rear: 25X11-12 4 PR Max pressure 7 psi

The first thing that jumps out at me is that the tires are physically smaller (which means less load carrying capacity at the same pressure) and that the new tires have a lower Ply Rating (which also means less load carrying capacity).

This should be cause for alarm!!

So I'm going to be doing a little digging. I went to the Carlisle website and found the 2 new tires. They have more information:

.
New Front: 25X8-12 4 PR Max Pressure 7 psi Max load 785# @ 50 mph, Max pressure 22 psi
New Rear: 25X11-12 4 PR Max pressure 7 psi Max Load 1050# @ 50 mph, Max Pressure 22 psi

What's missing here is if the max pressure corresponds to the max load. So I pulled out my Tire and Rim Yearbook (2005) and it indicates that indeed the pressure corresponding to the max load is 7 psi for a 3 star - AND the max speed is 50 mph. But most importantly, they use a Star System (1, 2 or 3 stars) not PR. - AND - they have the old tire sizes listed So let me add that information:

Old Front: 26X9-12 6 PR Specified inflation 10 psi,
TRA: 26X9-12, 3 Star: Max load 410# @ 7 psi, Max speed 50 mph
Old Rear: 26X11-12 6 PR Specified Inflation 12 psi
TRA: 26X11-12 3 Star: Max load 380# @ 7 psi, Max Speed 50 mph

New Front: 25X8-12 4 PR Max Pressure 7 psi
TRA: 25X8-12 3 Star: 340# @ 7 psi, Max speed 50 mph

New Rear: 25X11-12 4 PR Max pressure 7 psi
TRA: 25X8-12 3 Star: 455# @ 7 psi, Max speed 50 mph.

*********************************************************************************

At this point, I tried to make some sense of what was being published. Between the various tire manufacturers for these types of tire and The Tire and Rim Assocuiation, I was able to determine that the Star system isn't like the PR system - and that I just didn't have all the information I needed to make sense of it all - and it didn't look like I was going to find that information in the short term. So allow me to take my best estimate as to what pressure needs to be in the new tires:

New fronts: 13 psi.
New rears: 15 psi.

The above is based on maintaining the pressure split to get the same spring rate split in the tires. Those pressures should have about the same load carrying capacity as the old tires did.

******************************************************************************************
LancerPlayer,

In case you have the old tires, please look very carefully at the sidewalls and tell me what it says. Look at both sides. Copy all the load information EXACTLY and post it in this thread. Include if there are markings for Ply Rating (PR) and/or Stars (*, **, or ***)

Do the same thing on your new tires.

I'm asking you do to this to confirm some things I suspect are true: That the star system and the PR system have a correspondence, but it's different in that the PR system doesn't take into account the low pressures that these tires are supposed to be used at for trail riding.

I'm going to also ask you to look at the owners manual for your Polaris. There is likely some information about tires in it. That would be very helpful in sorting this out.

Thanks ahead of time.

Last edited by CapriRacer; 11/14/19 08:39 AM.

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